An Earth File is an XML description of a map. Creating an earth file is the
easiest way to configure a map and get up and running quickly. In the osgEarth
repository you will find dozens of sample earth files in the tests folder,
covering various topics and demonstrating various features. We encourage you to
explore and try them out!

This Earth File creates a geocentric Map named MyMap with a single
GeoTIFF image source called bluemarble. The driver attribute
tells osgEarth which of its plugins to use to use to load the image.
(osgEarth uses a plug-in framework to load different types of data
from different sources.)

Some of the sub-elements (under image) are particular to the selected
driver. To learn more about drivers and how to configure each one, please
refer to the Driver Reference Guide.

osgEarth supports maps with multiple image sources.
This allows you to create maps such as base layer with a transportation
overlay or provide high resolution insets for specific areas that sit
atop a lower resolution base map.

The above map provides two images from local data sources using the GDAL driver.
Order is important when defining multiple image sources: osgEarth renders them
in the order in which they appear in the Earth File.

Tip: relative paths within an Earth File are interpreted
as being relative to the Earth File itself.

This Earth File has a base bluemarble image as well as a elevation
grid that is loaded from a local GeoTIFF file. You can add as many elevation
layers as you like; osgEarth will combine them into a single mesh.

As with images, order is important - For example, if you have a base
elevation data source with low-resolution coverage of the entire world and
a high-resolution inset of a city, you need specify the base data FIRST,
followed by the high-resolution inset.

Some osgEarth drivers can generate elevation grids as well as imagery.

Note: osgEarth only supports single-channel 16-bit integer or 32-bit
floating point data for use in elevation layers.

Since osgEarth renders data on demand, it sometimes needs to do some work in
order to prepare a tile for display. The cache exists so that osgEarth can
save the results of this work for next time, instead of processing the tile
anew each time. This increases performance and avoids multiple downloads of
the same data.

This Earth File shows the most basic way to specify a cache for osgEarth.
This tells osgEarth to enable caching and to cache to the folder c:/osgearth_cache.
The cache path can be relative or absolute; relative paths are relative to the
Earth File itself.

There are many ways to configure caching; please refer to the section on Caching for
more details.